Poly(phenylene ether)s are commercially attractive materials because of their unique combination of physical, chemical, and electrical properties. Furthermore, the combination of poly(phenylene ether)s with other polymers or additives provides blends which result in improved overall properties including chemical resistance, high strength, and high flow. As new commercial applications are explored, higher purity poly(phenylene ether) materials are desired.
The processes most generally used to produce poly(phenylene ether)s involve the self-condensation of at least one monovalent phenol in the presence of an oxygen containing gas and a catalyst comprising a metal amine complex to produce resins typically within the intrinsic viscosity range of 0.35 to 0.65 deciliter per gram as measured in chloroform at 25° C. These processes are typically carried out in the presence of an organic solvent and the reaction is usually terminated by removal of the catalyst from the reaction mixture. The catalyst metal, after being converted into a soluble metal complex with the aid of a chelating agent, is removed from the polymer solution with standard extraction techniques, such as liquid-liquid extraction.
Various techniques of isolating and purifying poly(phenylene ether)s have been described. For example, GB 1219335 relates to a process for the purification and decolorizing of a poly(phenylene ether), where a solution of an aryl substituted poly(phenylene ether) is contacted with an ion exchange resin and an adsorbent which is alumina, charcoal, a metal silicate, or a mixture thereof. EP 0435023 teaches a method for removing volatile substances from poly(phenylene ether) blends by extruding with multiple stages of water injection followed by vacuum venting. US 2009/062478 relates to a method of preparing capped poly(arylene ether)s that includes washing the reaction mixture with a concentrated basic aqueous solution.
There remains a need for an improved method for purifying a poly(phenylene ether) that overcomes limitations associated with known processes. Such a process would desirably provide a poly(phenylene ether) composition that meets various purity specifications, specifically related to residual organic acid and/or amine impurities. Additionally, a preferred process would reduce or eliminate both organic acid and amine impurities using a single technique.